I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Some Recent Findings

Development of urinary organs in domestic cat during the embryonic and fetal periods[3] "The embryonic origin of the urogenital system came from the intermediate mesoderm. Kidney development involves three successive renal systems with a fast chronological overlap: the pronephro, the mesonephro, and the metanephro. Due to the lack of specific knowledge about this system in cats the present work aimed to describe their urinary organs development, focusing on the structures seen in pronephro, mesonephro, and metanephro during the embryonic and fetal stages of development. The techniques used in this study were: light microscopy, immunohistochemistry, scanning electron microscopy, and transmission electron microscopy. For that, embryos and fetuses from 12 pregnant mixed-breed domestic cats in different gestational stages were used to describe the proposed organs. The pronephro is present at early stages of embryonary development in embryos from 15 to 19 days with the presence of pronephro's corpuscles, ducts and tubules. The mesonephro is found, in general, between days 17 and 37, and contains mesonephric ducts, mesonephric tubules, and glomeruli. The metanephro is seen since 21 days of pregnancy with the presence of glomeruli, proximal and distal contorted tubules and at day 37, the cortex-medullary region is already differentiated. The evaluation of these structures enhances the knowledge about embryology of the urinary system in cats, aiding a better anatomical understanding of the system in the specie allowing the correlation with other species." renal

Assisted Reproduction in the Female Cat[4] "Assisted reproduction in the queen can range from simple ovulation induction to more advanced techniques such as in vitro fertilization. This article describes techniques available and the success associated with each." ART

Lipid Droplet Phase Transition in Freezing Cat Embryos and Oocytes Probed by Raman Spectroscopy[5] "Embryo and oocyte cryopreservation is a widely used technology for cryopreservation of genetic resources. One limitation of cryopreservation is the low tolerance to freezing observed for oocytes and embryos rich in lipid droplets. We apply Raman spectroscopy to investigate freezing of lipid droplets inside cumulus-oocyte complexes, mature oocytes, and early embryos of a domestic cat. Raman spectroscopy allows one to characterize the degree of lipid unsaturation, the lipid phase transition from the liquid-like disordered to solid-like ordered state, and the triglyceride polymorphic state. ...Raman spectroscopy is proved to be a promising tool for in situ monitoring of the lipid phase state in a single embryo/oocyte during its freezing." (Raman spectroscopy is a vibrational spectroscopic technique used to provide information on molecular vibrations and crystal structures.)

Follicular growth monitoring in the female cat during estrus[6] "This study was designed to describe follicular dynamics by transabdominal ultrasonography. Secondly, the stage of follicular growth was associated to behavioral and vaginal changes. Ovarian ultrasonography was performed during nine anovulatory and 12 ovulatory cycles. Forty-eight follicles were followed during anovulatory cycles: on the first day of estrus behavior, 4.8 ± 0.2 follicles (2 to 7 per female) of 2.3 ± 0.01 mm mean diameter were present. Follicular growth continued at a rate of 0.2 ± 0.04 mm per day. At least one follicle in the cohort reached a diameter greater than 3.0 mm."

More recent papers

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Development of external genitalia in fetal and neonatal domestic cats[7] "The female urogenital folds budded from each side of the genital tubercle and, gradually extended to the tip of the genital tubercle by the 6.8 cm stage in crown-rump length. Then, the well-developed urogenital folds ensheathed completely the genital tubercle to form the prepuce of clitoris and the labia, flanking the external opening of vagina as the folds of skin which were equivalent to the labia minora in humans. The genital swellings known to become the labia majora in humans were clearly recognized in the caudolateral region of the genital tubercle during the fetal stage. These swellings became flat and obscure after birth. Thus, in cats the genital swellings did not join to the formation of the labia in the same way as in humans. The sex difference in the external genitalia was first observed at the 3.2-3.3 cm stages. In the male, the anogenital raphe appeared and the caudal portion of the genital swellings moved and fused each other at the caudal region of the genital tubercle. In the female, both features were not easy to observe." genital

Additional Images

Historic Images

Historic Disclaimer - information about historic embryology pages

Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers)

Fig. 210. Normal well-preserved cat fetus

Fig. 211. Normal poorly preserved cat fetus of approximately the same length

Plate 4. Cat Fetus and Placenta

Fig. 297. Transverse section through the thoracic region of a cat embryo of 25 mm